Magnetoresistance effect film and production process thereof

ABSTRACT

A magnetoresistance effect film is disclosed. This magnetoresistance effect film comprises a substrate, at least two ferromagnetic thin films stacked one over the other on the substrate with a non-magnetic thin film interposed therebetween, and an antiferromagnetic thin film arranged adjacent to one of the ferromagnetic thin films. The antiferromagnetic thin film is a superlattice formed of at least two oxide antiferromagnetic materials selected from NiO, Ni x  Co 1-x  O (0.1≦x≦0.9) and C o  O. A biasing magnetic field Hr applied to the one ferromagnetic thin film located adjacent the antiferromagnetic thin film is greater than coercive magnetic force Hc2 of the other ferromagnetic thin film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetoresistance effect film useful in amagnetoresistance effect device employed, for example, to read as signalinformation or the like recorded on a magnetic recording medium or thelike, and more specifically to a magnetoresistance effect film whichshows a large rate of change in resistance in a small external magneticfields.

2. Description of the Related Art

In recent years, high sensitization of magnetic sensors and highdensification in magnetic recording are under way. Keeping step withthis, active developments have been conducted with respect tomagnetoresistance effect magnetic sensors (hereinafter called "MRsensors") and magnetoresistance effect magnetic heads (hereinaftercalled "MR heads"). MR sensors and MR heads each detect a change inresistance at a read sensor made of a magnetic material to read anexternal magnetic field signal. In these MR sensors and MR heads, theirreproduction outputs do not depend on their relative speeds withrecording media, leading to the merit that the MR sensors have highsensitivity and the MR heads provides high outputs in high-densitymagnetic recording.

Proposed recently is a magnetoresistance effect film having at least twoferromagnetic thin films stacked one over the other with a non-magneticthin film interposed therebetween and an antiferromagnetic thin filmarranged adjacent to one of the ferromagnetic thin films so that saidone ferromagnetic thin film is provided with antimagnetic force. When anexternal magnetic field is applied to this magnetoresistance effect thinfilm, the one ferromagnetic thin film and the other ferromagnetic thinfilm are magnetized in different directions under the external magneticfield, whereby a change takes place in resistance (Phys. Rev. B, 43,1297, 1991; Japanese Patent Laid-Open No. 358310/1992).

Although the magnetoresistance effect device of the precedingapplication is operable in small external magnetic fields, each signalmagnetic field must be applied in the direction of an easy magnetizationaxis when it is used as a practical sensor or magnetic head. It istherefore accompanied by the problems that, when employed as a sensor,no change in resistance is exhibited around the zero magnetic field andnon-linearity such as when a Barkhausen jump appears.

Further, there is a ferromagnetic interaction between the ferromagneticthin films which are located adjacent to each other with thenon-magnetic thin film interposed therebetween, resulting in the problemthat a linear range in an MR curve is shifted from the zero magneticfield.

Moreover, it is necessary to use FeMn, a material having poor corrosionresistance, as the antiferromagnetic thin film. This involves theproblem that upon practice, an additional measure is needed such asincorporation of an additive or application of a protective film.

When an oxide antiferromagnetic material excellent in corrosionresistance is formed into a film at a room temperature to provide theantiferromagnetic thin film, on the other hand, the biasing magneticfield is small so that the coercive force of the adjacent ferromagneticthin film becomes large. This has led to the problem that amagnetization anti-parallel state can hardly be obtained between theferromagnetic thin films.

Because of the construction that a change in resistance is obtainedbasically by using a change in the length of mean free path ofconduction electrons across the three layers of themagnetic/non-magnetic/magnetic films, the above-described conventionalmagnetoresistance effect films are accompanied by the problem that theyshow smaller rates of change in resistance compared withmagnetoresistance effect films having multilayer structures and calledthe "coupling type".

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetoresistanceeffect film which linearly shows a large change in resistance around thezero magnetic field, is operable at high temperatures and moreover, isexcellent in corrosion resistance.

To achieve the above object, the present invention provides amagnetoresistance effect film comprising a substrate, at least twoferromagnetic thin films stacked one over the other on said substratewith a non-magnetic thin film interposed therebetween, and anantiferromagnetic thin film arranged adjacent to one of saidferromagnetic thin films, said antiferromagnetic thin film being asuperlattice formed of at least two oxide antiferromagnetic materialsselected from NiO, Ni_(x) Co_(1-x) O (0.1≦x≦0.9) and C_(o) O, and abiasing magnetic field Hr applied to said one ferromagnetic thin filmlocated adjacent said antiferromagnetic thin film being greater thancoercive magnetic force Hc2 of the other ferromagnetic thin film.

The present invention also provides a process for producing amagnetoresistance effect film by forming, on a substrate, at least twoferromagnetic thin films stacked one over with a non-magnetic thin filminterposed therebetween, and an antiferromagnetic thin film arrangedadjacent to one of said ferromagnetic thin films, said antiferromagneticthin film being a superlattice formed of at least two oxideantiferromagnetic materials selected from NiO, Ni_(x) Co_(1-x) O(0.1≦x≦0.9) and C_(o) O, and a biasing magnetic field Hr applied to saidone ferromagnetic thin film located adjacent said antiferromagnetic thinfilm being greater than coercive magnetic force Hc2 of the otherferromagnetic thin film, wherein a magnetic field applied duringformation of said one ferromagnetic thin film and a magnetic fieldapplied during formation of said other ferromagnetic thin film arerotated over 90 degrees from each other so that easy magnetization axesof said ferromagnetic thin films are perpendicular to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a B-H curve explaining the principle of operation of amagnetoresistance effect film according to the present invention;

FIG. 2 is an R-H curve explaining the principle of operation of themagnetoresistance effect film according to the present invention;

FIG. 3 is an exploded perspective view illustrating the construction ofan illustrative magnetoresistance sensor according to the presentinvention;

FIG. 4A is a cross-sectional view of a magnetoresistance effect filmaccording to one embodiment of the present invention;

FIG. 4B is a cross-sectional view of a magnetoresistive effect filmaccording to another embodiment of the present invention.

FIG. 5 is a B-H curve of the magnetoresistance effect film according tothe present invention;

FIG. 6 is an MR curve of the magnetoresistance effect film according tothe present invention; and

FIG. 7 diagrammatically shows temperature characteristics of the rate ofchange in resistance of the magnetoresistance effect film according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 illustrates the construction of the illustrativemagnetoresistance sensor according to the present invention.Ferromagnetic thin films 2,3 are arranged with their easy magnetizationaxes extending at a right angle relative to each other and with anon-magnetic thin film 1 interposed therebetween. At this stage, one ofthe ferromagnetic thin films, that is, the ferromagnetic thin film 3 hasbeen applied with unidirectional anisotropy by the adjacentantiferromagnetic thin film 5. The magnetic field of each signal from amagnetic recording medium is set so that the magnetic field becomesperpendicular to the direction of the easy magnetization axis of theother ferromagnetic thin film 2. In the direction of the easymagnetization axis of the other ferromagnetic thin film 2, anantiferromagnetic thin film or permanent magnetic thin film 6 may beadditionally arranged adjacent the other ferromagnetic thin film 2 asshown in FIG. 3, whereby the direction of magnetization is directedsolely in the direction of the easy magnetization axis. Since thedirection of magnetization of the ferromagnetic thin film 2 responds toeach signal magnetic field and rotates, the resistance is changed sothat the magnetic field is detected.

For the magnetoresistance effect film according to the presentinvention, it is essential that the antiferromagnetic thin film isformed adjacent the one ferromagnetic thin film to apply exchangebiasing force to the one ferromagnetic thin film, because according tothe principle of the present invention, a maximum resistance isexhibited when the directions of magnetization of the adjacentferromagnetic thin films become opposite to each other. Describedspecifically, when an external magnetic field is between the anisotropicmagnetic field of the ferromagnetic thin film and the antimagnetic forceof the one ferromagnetic thin film (Hk2<H<Hr) as illustrated in FIG. 1,the direction of magnetization of the adjacent ferromagnetic thin filmsbecome opposite to each other, resulting in an increase in resistance inthe present invention.

A description will now be made of a relationship among an externalmagnetic field, coercive force and the direction of magnetization.

As is shown in FIG. 1, the antimagnetic force of the one ferromagneticthin film exchange-biased by the adjacent antiferromagnetic thin film isrepresented by Hr, the coercive force of the other ferromagnetic thinfilm by Hc2, and the anisotropic magnetic field by Hk2 (0<Hk2<Hr).First, an external field H is applied at such an intensity as satisfyingH<-Hk2 (I). At this time, the directions of magnetization of theferromagnetic thin films 2,3 are negative (-) like H. When the externalmagnetic field is then progressively reduced, the magnetization of theferromagnetic thin film 2 is rotated in a positive (+) direction in-Hk2<H<Hk2 (II), and the directions of magnetization of theferromagnetic thin films 2,3 become opposite to each other in the range(III) of Hk2<H<Hr. In the range (IV) of Hr<H where the external magneticfield has been intensified further, the magnetization of theferromagnetic thin film 3 is also reversed so that the directions ofmagnetization of the ferromagnetic thin films 2 and 3 are both positive(+).

As is shown in FIG. 2, the resistance of the above film changesdepending on the relative directions of magnetization of theferromagnetic thin films 2 and 3, linearly changes around the zeromagnetic field, and takes a maximum value (Rmax) in the range (III).

The antiferromagnetic material employed for the antiferromagnetic thinfilm 5 in the present invention specifically has a superlatticestructure 5a, 5b, . . . , 5n, 5n+1 . . . in which at least two oxideantiferromagnetic materials 5a, 5b selected from NiO, Ni_(x) Co_(1-x) Oand CoO are alternately stacked, in which x stands for a positive valueof 0.1 to 0.9. The film thickness ratio of the individual layers in sucha superlattice can be set so that the volume molar ratio of nickel tocobalt in the superlattice falls within a range of 1 to 6. This makesthe superlattice act as an antiferromagnetic material at 100° C. andhigher.

The upper limit of the film thickness of the antiferromagnetic thin filmis 1,000 Å. Although no particular lower limit is imposed on thethickness of the antiferromagnetic thin film, it is preferred to set thelower limit at 100 Å or greater for better crystallinity because thecrystallinity of the superlattice of the antiferromagnetic materialsignificantly affects the intensity of the exchange-coupling magneticfield which is applied to the adjacent ferromagnetic thin film. Further,it is preferred to limit the unit film thickness of eachantiferromagnetic layer forming the antiferromagnetic superlattice to 50Å or smaller. Inside the above ranges, interactions at interfacesbetween the individual antiferromagnetic layers are significantlyreflected to characteristics of the superlattice. This makes it possibleto apply a large biasing magnetic field to the adjacent ferromagneticthin film. In addition, formation of the films with the substratetemperature controlled to 100°-300° C. results in improved crystallinityso that the biasing magnetic field is intensified. For the formation ofthe films, a film-forming process such as vacuum deposition, sputteringor molecular beam epitaxy (MBE) is preferred. Preferred as the materialof the substrate is glass, Si, MgO, Al₂ O₃, GaAs, ferrite, CaTi₂ O₃,BaTi₂ O₃, Al₂ O₃ --TiC or the like.

Although no particular limitation is imposed on the ferromagneticmaterial used for the ferromagnetic thin films in the present invention,preferred specific examples include Fe, Ni, Co, Mn, Cr, Dy, Er, Nd, Tb,Tm, Ge and Gd. As alloys and compounds containing these elements,preferred examples include Fe--Si, Fe--Ni, Fe--Co, Fe--Gd, Ni--Fe--Co,Ni--Fe--Mo, Fe--Al--Si (sendust), Fe--Y, Fe--Mn, Cr--Sb, Co-baseamorphous alloys, Co--Pt, Fe--Al, Fe--C, Mn--Sb, Ni--Mn and ferrite.

In the present invention, the magnetic thin films are formed byselecting appropriate magnetic materials from the materials exemplifiedabove. In particular, selection of a material for the otherferromagnetic thin film which is not located adjacent theantiferromagnetic thin film so that the anisotropic magnetic field Hk2is greater than its coercive force Hc2 realizes the construction of themagnetoresistance effect thin film according to the present invention.

Further, the anisotropic magnetic field can be increased by making thefilm thickness smaller. For example, the anisotropic magnetic field Hk2can be made greater than the coercive force Hc2 when a ferromagneticthin film of NiFe is formed with a thickness of 10 Å or so.

In such a magnetoresistance effect film, the easy magnetization axis ofeach ferromagnetic thin film is perpendicular to the direction of asignal magnetic field. The magnetoresistance effect film can be producedby forming the ferromagnetic thin films under such a magnetic field thatthe anisotropic magnetic field Hk2 of the ferromagnetic thin films inthe direction of the applied signal magnetic field satisfies thefollowing inequality: Hc2<Hk2<Hr. Specifically, magnetic fields appliedupon formation of the ferromagnetic thin films are rotated over 90degrees or the substrate is rotated over 90 degrees in a magnetic fieldso that the easy magnetization axis of the one ferromagnetic filmlocated adjacent the antiferromagnetic film and the easy magnetizationaxis of the other ferromagnetic film located adjacent the oneferromagnetic thin film with the non-magnetic film interposedtherebetween cross at a right angle.

The upper limit of the thickness of each ferromagnetic thin film ispreferably 200 Å. A film thickness greater than 200 Å is wasting uponformation of the film and uneconomical, because the change in themagnetic resistance of the magnetoresistance effect film does notincrease as the film thickness becomes greater. Although no particularlower limitation is imposed on the thickness of the ferromagnetic thinfilm, a film thickness smaller than 30 Å results in greater surfacescattering effect of conduction electrons so that the change in magneticresistance becomes smaller. On the other hand, a film thickness of 30 Åor greater makes it easier to maintain the film thickness uniform andalso leads to better characteristics. It is also possible to prevent thesaturation magnetization from becoming unduly small.

The coercive force of the one ferromagnetic thin film located adjacentthe antiferromagnetic thin film can be reduced by forming it incontinuation with the antiferromagnetic thin film while maintaining thetemperature of the substrate at 100°-300° C.

Further, formation of a Co or Co-base alloy layer 8 at the interfacebetween each ferromagnetic thin film 2,3 and the non-magnetic thin film1 increases the probability of interfacial scattering of conductionelectrons so that a still greater change in magnetic resistance can beobtained. The lower limit of the film thickness of the Co or Co-basealloy layer 8 is 5 Å. A smaller film thickness reduces the effect of theinterposition of the film and further, makes it difficult to control thefilm thickness. Although no particular upper limitation is imposed onthe thickness of the interposed film, about 30 Å or so are preferred. Athickness greater than this level results in appearance of a hysteresisin outputs in an operation range of the magnetoresistance effect device.

By arranging an additional antiferromagnetic thin film or a permanentmagnet thin film in adjacent to and in the direction of easymagnetization of the ferromagnetic thin film for detecting an externalmagnetic field, that is, the other ferromagnetic thin film which is notlocated adjacent the antiferromagnetic layer in the abovemagnetoresistance effect film, the magnetic domains can be stabilized sothat non-linear outputs such as Barkhausen jumps can be avoided. As thematerial of the additional antiferromagnetic thin film employed for thestabilization of the magnetic domains, FeMn, NiMn, NiO, CoO, FeO, Fe₂O₃, Cro, MnO or the like is preferred. On the other hand, as thematerial of the permanent magnet thin film, CoCr, CoCrTa, CoCrTaPt,CoCrPt, CoNiPt, CoNiCr, CoCrPtSi, FeCoCr or the like is preferred.Further, Cr or the like can be used as a primer for the permanent magnetthin film.

The non-magnetic thin film serves to reduce the magnetic interactionbetween the ferromagnetic thin films. No particular limitation isimposed on its material. A suitable material can be selected fromvarious metallic materials, semimetallic nonmagnetic materials andnon-metallic non-magnetic materials.

Preferred examples of metallic non-magnetic materials include Au, Ag,Cu, Pt, Al, Mg, Mo, Zn, Nb, Ta, V, Hf, Sb, Zr, Ga, Ti, Sn and Pb andalloys thereof. Preferred examples of semimetallic non-magneticmaterials include SiO₂, SiO, SiN, Al₂ O₃, ZnO, MgO and TiN and thoseobtained by one or more elements to such materials.

From experimental results, the desired thickness of the non-magneticthin film is 20 to 35 Å. A film thickness greater than 40 Å generallyresults in concentration of a current at the non-magnetic thin film sothat the spin-dependent electron-scattering effect relatively becomessmaller. This results in a reduction in the rate of change in themagnetoresistance. On the other hand, a film thickness smaller than 20 Åresults in unduly large magnetic interaction between the ferromagneticthin films and unavoidably leads to occurrence of a magnetically directcontact state (pinholes). Accordingly, it becomes difficult to produce adifference in the direction of magnetization between both theferromagnetic thin films.

The thicknesses of the magnetic and non-magnetic thin films can bemeasured by a transmission electron microscope, a scanning electronmicroscope, an Auger electron spectroscopic analyzer or the like.Further, the crystalline structure of each thin film can be ascertainedby X-ray diffraction, fast electron-beam diffraction or the like.

In the magnetoresistance effect device according to the presentinvention, no particular limitation is imposed on the number N ofrepeated stacking of artificial lattice films. This number can be chosenas desired depending on the target rate of change in magnetoresistance.However, the antiferromagnetic thin film has a large resistivity andimpairs the effect of the stacking. It is therefore preferred to havethe structure of antiferromagnetic layer/ferromagneticlayer/non-magnetic layer/ferromagnetic layer/non-magneticlayer/ferromagnetic layer/antiferromagnetic layer.

Further, it is also possible to arrange an anti-oxidizing film such as asilicon nitride, silicon oxide or aluminum oxide film over the surfaceof the uppermost layer, that is, the ferromagnetic thin film. Inaddition, metallic conductive layers can also be provided lead outelectrodes.

As magnetic characteristics of ferromagnetic thin films contained in amagnetoresistance effect device cannot be measured directly, they areusually measured as will be described below. Namely, ferromagnetic thinfilms are alternately formed with non-magnetic thin films until thetotal thickness of the ferromagnetic thin films reaches 500-1,000 Å orso to prepare a sample for the measurement, and magnetic characteristicsare measured with respect to the sample. In this case, the thickness ofeach ferromagnetic thin film, the thickness of the non-magnetic thinfilm and the composition of the non-magnetic thin film are the same asthose of the magnetoresistance effect device.

The magnetoresistance effect device according to the present inventionwill be described specifically by examples. FIG. 4A is a cross-sectionalview of an artificial lattice film 7 according to one embodiment of thepresent invention. In FIG. 4, the artificial lattice film 7 has beenconstructed by successively stacking, on a glass substrate 4, anantiferromagnetic thin film 5 having a superlattice structure formed ofat least two oxide anti-ferromagnetic materials, one of ferromagneticthin films, namely, the one ferromagnetic thin film 3, a non-magneticthin film 1, the other ferromagnetic thin film 2, and anantiferromagnetic thin film 6.

In the above-described artificial lattice film 7, the non-magnetic thinfilm 1 is interposed between the adjacent two ferromagnetic thin films2,3. In addition, an additional antiferromagnetic thin film or apermanent magnet thin film can be arranged in adjacent to theferromagnetic thin film 2.

The glass substrate 4 is placed in a film-forming apparatus, followed byevacuation to the order of 10⁻⁷ Torr. The substrate temperature wasraised to 150° C. The antiferromagnetic thin film 5 was first formed toa thickness of 500 Å and the ferromagnetic thin film 3 was then formedwith NiFe, whereby an exchange-coupling film was formed. The temperatureof the substrate was allowed to cool down to room temperature, and thenon-magnetic thin film 1 and the other ferromagnetic thin layer 2 wereformed to obtain a magnetoresistance effect film.

The artificial lattice film 7 was formed at a film-forming speed ofabout 2.2 to 3.5 Å/sec. As shown in FIG. 4B, an alloy layer 8 isinterposed between each ferromagnetic thin film 2, 3 and thenon-magnetic thin film 1.

Incidentally, when indicated, for example, as (CoO(10)/NiO(10))₂₅/NiFe(100)/Cu(25)/NiFe(100), it is meant that a superlattice 5a, 5b, . .. 5n, 5n+1 was formed by alternately stacking CoO and NiO thin films 10Å by 10 Å 25 times on a substrate and an Ni80%-Fe20% alloy thin film of100 Å, a Cu thin film of 25 Å, and an Ni80%-Fe20% thin film of 100 Åwere then successively formed.

Measurement of magnetization was conducted by a vibrating samplemagnetometer. For the measurement of resistance, a sample in a shape of1.0×10 mm² was prepared from the sample, and the resistance was measuredby the 4 terminal method when the external magnetic field was changedfrom -500 to 500 Oe while applying an external magnetic field in theplane in a direction perpendicular to a current. From the resistances someasured, the rate of change in the magnetic resistance, ΔR/R, wascalculated. The rate of change in resistance ΔR/R was calculated inaccordance with the following formula: ##EQU1## Where, Rmax: maximumresistance, and

Rmin: minimum resistance.

EXAMPLES 1-4

The constructions of the thus-produced magnetoresistance effect filmsare shown in the following table.

    ______________________________________    Example 1       Glass/(CoO(10)/NiO(10)).sub.25 /                    NiFe(100)/Cu(25)/NiFe(100)    Example 2       Glass/(CoO(8)/NiO(12)).sub.25 /                    NiFe(100)/Cu(25)/NiFe(100)    Example 3       Glass/(CoO(5)/NiO(15)).sub.25 /                    NiFe(100)/Cu(25)/NiFe(100)    Example 4       Glass/(CoO(3)/NiO(18)).sub.25 /                    NiFe(100)/Cu(25)/NiFe(100)    ______________________________________

By setting the thickness of the non-magnetic thin film at 25 Å, a rateof change in resistivity of 3.8% or so was obtained. By interposing Coat an interface between the ferromagnetic thin film (NiFe) and thenon-magnetic thin film (Cu), a rate of change in resistivity of 6% wasobtained. A B-H curve and M-R curve of the artificial lattice film(No. 1) are shown in FIGS. 5 and 6, respectively. Further, it isunderstood that a magnetoresistance effect device operable at stillhigher temperatures can be obtained by setting the film thickness ratioof NiO to CoO in an antiferromagnetic thin film at 1.5 (No. 2), 3 (No.3) or 6 (No. 4) as shown in FIG. 7.

In the above-described embodiments, the super-lattice of CoO and NiO wasused as the antiferromagnetic thin film 5. With magnetoresistance effectdevices obtained by substituting a superlattice of Ni_(x) Co_(1-x) O andNiO, (N_(i) O/N_(i).sbsb.x C_(o).sbsb.1-x O) a superlattice of Ni_(x)Co_(1-x) O and CoO (CoO/N_(i).sbsb.x C_(o).sbsb.1-x O) and asuperlattice of Ni_(x) Co_(1-x) O, NiO and CoO, respectively, rates ofchange in resistance in a range of 4% to 7% were also obtained.

The film formation was conducted in such a state that NdFeB magnets werearranged on opposite sides of a glass substrate and an external magneticfield of approximately 400 Oe was applied in parallel with the glasssubstrate. Measurement of a B-H curve of the resultant sample indicatedthat the direction in which the magnetic field was applied during thefilm formation became an easy magnetization axis of an artificiallattice, that is, a NiFe layer.

What is claimed is:
 1. A magnetoresistive effect film comprising asubstrate, at least two ferromagnetic thin films stacked one over theother on said substrate with a non-magnetic thin film interposedtherebetween, and an antiferromagnetic thin film arranged adjacent toone of said ferromagnetic thin films, said antiferromagnetic thin filmbeing a superlattice formed from a combination of at least two oxideantiferromagnetic materials, said combination selected from NiO/Ni_(x)Co_(1-x) O (0.1<x<0.9) and CoO/Ni_(x) Co_(1-x) O (0.1<x<0.9), and saidone ferromagnetic thin film located adjacent to said antiferromagneticthin film being magnetically biased thereby so that a biasing magneticfield Hr of said one ferromagnetic thin film is greater than a coercivemagnetic force Hc2 of the other ferromagnetic thin film.
 2. Amagnetoresistive effect film comprising a substrate, at least twoferromagnetic thin films stacked one over the other on said substratewith a non-magnetic thin film interposed therebetween, and anantiferromagnetic thin film arranged adjacent to one of saidferromagnetic thin films, wherein said antiferromagnetic film is asuperlattice of oxides formed from a combination of at least two oxideantiferromagnetic materials, said combination selected from NiO/Ni_(x)Co_(1-x) O (0.1<x<0.9) and CoO/Ni_(x) Co_(1-x) O (0.1<x<0.9), the numberratio of Ni atoms to Co atoms ranges from 1.5 to 6, and said oneferromagnetic thin film located adjacent to said antiferromagnetic thinfilm is magnetically biased thereby so that a biasing magnetic field Hrof said one ferromagnetic thin film is greater than a coercive magneticforce Hc2 of the other ferromagnetic thin film.
 3. A magnetoresistanceeffect film according to claim 2, wherein said non-magnetic thin filmhas a thickness of 20 to 35 Å.
 4. A magnetoresistance effect filmaccording to claim 2 or 3, wherein the biasing magnetic field Hr and thecoercive magnetic force Hc2 satisfy the following inequality:

    Hc2<Hk2<Hr

where Hk2 is an anisotropic magnetic field.
 5. A magnetoresistanceeffect film according to claim 2 or 3, wherein said ferromagnetic thinfilms are made of a material composed as a principal component of Ni,Fe, Co, FeCo, NiFe, NiFeCo or an alloy containing one or more of Ni, Fe,Co, FeCo, NiFe and NiFeCo.
 6. A magnetoresistance effect film accordingto claim 2 or 3, further comprising a Co or Co-base alloy film of 5 to30 Å in thickness interposed between said non-magnetic thin film and atleast one of said ferromagnetic thin films.
 7. A magnetoresistanceeffect film according to claim 2 or 3, wherein the other ferromagneticthin film which is not located adjacent said antiferromagnetic thin filmhas been formed into single domains by using an antiferromagnetic thinfilm or a permanent magnet thin film.